1. Field of the Invention
The present invention relates to an assistant light source and front-light, particularly to an assistant light source and front-light having a function of changing light of spot light source to light of line light source.
2. Description of Related Art
A reflective or transflective liquid crystal display device includes a liquid crystal cell having a pair of opposed substrates and a liquid crystal layer sandwiched between these opposed substrates, and has a so-called display function in a reflective mode in which an image is displayed using external light. This type of device displays an image in the same reflective mode even if external light is weak, and it is therefore provided with a front-light which is a surface illumination apparatus supplying light to the liquid crystal cell from the display side of the liquid crystal cell.
This front-light principally comprises a light guide placed facing and substantially in parallel to the surface on the display side of the liquid crystal cell, and an edge-light (side light), placed at end faces of the light guide, for emitting light to the end face. The light from the edge-light transmits through the light guide, with its propagation direction changed to the underside of the light guide facing the liquid crystal cell in the light guide, that is, the surface of the display side of the liquid crystal cell and enters the liquid crystal cell.
The edge-light is an assistant light source for the front-light and principally comprises an elongated cylindrical light stick for introducing light into the light guide and a spot light source arranged on both sides of the light stick, for emitting light to the light stick. As the spot light source, an LED is normally used. The edge-light in such a configuration converts light from the LED which is a spot light source to light from a line light source by the light stick and guides the converted light to the light guide.
The light stick in the edge-light is provided with a plurality of prisms on the face opposed to the end face of the light guide and the light from the edge-light is emitted substantially perpendicular to the end face of the light guide through these prisms (Japanese Laid-Open Patent Publication No. 2001-345006 (paragraph numbers [0004] and [0005])).
However, it is an actual situation that the conventional edge-light which is an assistant light source for a front-light is unable to emit light substantially perpendicular to the light guide from the light emitting face of the light stick. Therefore, the conventional edge-light cannot emit light to the light guide efficiently.